Abstract

Endosymbiotic bacteria of the genus Wolbachia infect a number of invertebrate species in which they induce various
alterations in host reproduction, mainly cytoplasmic incompatibility (CI). In contrast to most other maternally transmitted
parasites, manipulation of host reproduction makes the spread of Wolbachia possible even if they induce a physiological
cost on their hosts. Current studies have shown that fitness consequences of Wolbachia infection could range from positive
(mutualist) to negative (parasitic) but, in most cases, Wolbachia do not have strong deleterious effects on host fitness and
the status of association remains unclear. Here, we show that in the Drosophila parasitoid wasp Leptopilina heterotoma,
Wolbachia infection has a negative impact on several host fitness traits of both sexes. Fecundity, adult survival and
locomotor performance are significantly reduced, whereas circadian rhythm, development time and offspring sex-ratio are
not affected. Although the cost of bacterial infection can be overcome by effects on host reproduction i.e. cytoplasmic
incompatibility, it could influence the spread of the bacterium at the early stages of the invasion process. Clearly, results
underline the wide spectrum of phenotypic effects of Wolbachia infection and, to our knowledge, Wolbachia infection of
L. heterotoma appears to be one of the most virulent that has ever been observed in insects.